Species

Darwin and the Darwinians 175

All the foregoing rules and aids and difficulties in classification may be explained,

if I do not greatly deceive myself, on the view that the Natural System is founded on

descent with modification;—that the characters which naturalists consider as showing

true affinity between any two or more species, are those which have been inherited

from a common parent, all true classification being genealogical;—that community

of descent is the hidden bond which naturalists have been unconsciously seeking, and

not some unknown plan of creation, or the enunciation of general propositions, and the

mere putting together and separating objects more or less alike.

But I must explain my meaning more fully. I believe that the arrangement of the

groups within each class, in due subordination and relation to each other, must be

strictly genealogical in order to be natural; but that the amount of difference in the

several branches or groups, though allied in the same degree in blood to their common

progenitor, may differ greatly, being due to the different degrees of modification which

they have undergone; and this is expressed by the forms being ranked under different

genera, families, sections, or orders.^72

Given that there is some continuing dispute over whether or not Darwin was a
cladist,^73 it is worth stating here my view that Padian is right—for Darwin in this
last passage classification is necessarily natural only if it matches genealogy,^74 but
it may also be represented as well in terms of grade of organization. If it is, though,
such grades must not trim away the genealogical relationships. Darwin was not a
cladist,^75 but he was pretty close to it. However, he recognizes the practical necessity
of representing overall differences in a classification scheme. It’s just not the same as
saying these differences are part of a natural classification; this point shall become
significant in the argument presented in the final chapters. But even if Darwin were
an “eclectic” in his approach to classification as Mayr suggests, this would be due
to the fact that he had not yet completely worked out the implications of his view of
species related by common descent.
Darwin then summarizes the difference between the process by which things
have evolved and the patterns that diagnose them—his argument is remarkably simi-
lar to the so-called “father of cladistics,” Willi Hennig’s, view on “reciprocal illumi-
nation,” in which he argues that knowledge of groups illuminates the uncovering of
the knowledge of other groups, which then help refine the initial groups:^76

With species in a state of nature, every naturalist has in fact brought descent into his

classification; for he includes in his lowest grade, that of species, the two sexes; and

how enormously these sometimes differ in the most important characters, is known

to every naturalist: scarcely a single fact can be predicated in common of the adult

males and hermaphrodites of certain cirripedes, and yet no one dreams of separating

them. ... The naturalist includes as one species the various larval stages of the same

(^72) Op. cit., 323.
(^73) Mayr 1982, 209–213, Mayr 1994.
(^74) Padian 1999.
(^75) Cladism is a term that denotes a taxonomic methodology of classifying in terms of shared ancestry or
characters that derive from shared ancestry, properly known as “phylogenetic systematics,” developed
in the 1950s. It is strictly anachronistic to apply to Darwin terms that are only meaningful to describe
a later school of thought.
(^76) Hennig 1966, 21f, 148, 206, 222.